Author: F.M. Poli

Abstract: Recently published scenarios for fully non-inductive startup and operation on the National Spherical Torus eXperiment Upgrade (NSTX-U) [Menard J et al 2012 Nucl. Fusion 52 083015] show Electron Cyclotron Resonance Heating (ECRH) as an important component in preparing a target plasma for efficient High Harmonic Fast Wave and Neutral Beam heating. An extensive modelling effort of the propagation and absorption of EC waves in the evolving plasma is required to define the most effective window of operation, and to optimize the launcher geometry for maximal heating and current drive during this window. Here, we extend a previous optimization of 01-mode ECRH on NSTX-U to account for the full time-dependent performance of the ECRH using simulations performed with TRANSP, which self-consistently evolves the plasma equilibrium in time. It is found that time-dependent effects play a significant role in the effectiveness of the ECRH, particularly those related to the evolution of the density
profile, which are not captured by analysis on static profiles. The optimal injection angle, pointed 3° above the poloidal midplane and 4·:· in the toroidal direction, belongs to a class of injection angles robust to alterations in the density rampup, making it useful for a broad range of experimental conditions.

Submitted to: Plasma Physics and Controlled Fusion
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